Water soluble developer

ABSTRACT

A METHOD FOR DETECTING FLAWS AND OTHER SURFACE DISCONTINUTIES BY THE LIQUID PENETRANT TECHNIQUE WHEREIN AN AQUEOUS SOLUTION OF A WATER SOLUBLE CRYSTALLINE SUBSTANCE AND A WATER DISPERSIBLE SURFACTANT SERVES AS THE DEVELOPER FOR ENCHANCING THE VISIBILITY OF FLAW INDICATIONS GENERATED BY THE LIQUID PENETRANT. SAID PENETRANT PREFERABLY CONTAINS A VISIBLE OR FLUORESCENT DYE DISSOLVED THEREIN AND IS OF AN OILY TYPE WHICH ITSELF IS NOT SELFEMULSIFYINGT AND IS SUBSTANTIALLY FREE OF ANY ADDED EMULSIFYING AGENT. THE DEVELOPER, UPON THE EVAPORATION OR DRIVING OFF OF THE WATER, FORMS AN ADHERENT FIL, OR LATTICE LAYER, THAT IS PERMEABLE TO THE LIUQID PENETRANT RESIDUE ENTRAPPED IN ANY SURFACE DISCONTAINUITY SO AS TO CAUSE THE PENETRANT RESIDUE TO BE DRAWN BY CAPILLARITY OR OTHERWISE INTO SAID FILM AND FORM THEREIN FLAW INDICATIONS OF HIGH FIDELITY AND RESOLUTION THAT MAY BE EASILY DETECTED UPON INSPECTION. THE AQUEOUS DEVELOPER OF THIS INVENTION CAN OPTIONALLY INCLUDE FILM FORMING INGREDIENTS THAT EFFECTIVELY CONTROL THE SIZE OF CRYSTALS FORMED UPON DRYING; SEQUESTERING AGENTS FOR USE WITH HARD WATER; AND CORROSION INHIBITING AGENTS; BUT THE RESULTING FILM OR LATTICE LAYER IN ALL CASES IS ENTIRELY WATER SOLUBLE SO THAT THE SURFACE OF THE TEST PIECE CAN BE ADEQUATELY CLEANED BY THE USE OF WATER ALONE AT THE COMPLETION OF THE INSEPCTION STEP.

United States Patent Office 3,561,262 Patented Feb. 9, 1971 3,561,262 WATER SOLUBLE DEVELOPER James S. Borucki, Chicago, and Bruce C. Graham, Arlington Heights, 111., assignors to Magnaflux Corporation, Chicago, Ill., a corporation of Delaware No Drawing. Filed Oct. 26, 1967, Ser. No. 678,176 Int. Cl. Gllln 19/08 US. Cl. 73104 12 Claims ABSTRACT OF THE DISCLOSURE A method for detecting flaws and other surface discontinuities by the liquid penetrant technique wherein an aqueous solution of a water soluble crystalline substance and a water dispersible surfactant serves as the developer for enhancing the visibility of flaw indications generated by the liquid penetrant. Said penetrant preferably contains a visible or fluorescent dye dissolved therein and is of an oily type which itself is not self emulsifying and is substantially free of any added emulsifying agent. The developer, upon the evaporation or driving off of the water, forms an adherent film, or lattice layer, that is permeable to the liquid penetrant residue entrapped in any surface discontinuity so as to cause the penetrant residue to be drawn by capillarity or otherwise into said film and form therein flaw indications of high fidelity and resolution that may be easily detected upon inspection. The aqueous developer of this invention can optionally include film forming ingredients that effectively control the size of crystals formed upon drying; sequestering agents for use with hard water; and corrosion inhibiting agents; but the resulting film or lattice layer in all cases is entirely water soluble so that the surface of the test piece can be adequately cleaned by the use of water alone at the completion of the inspection step.

CROSS-REFERENCE TO RELATED APPLICATION pigmented developer, whether the liquid is water or an organic solvent, the pigment left behind on the surface of the test piece after development and inspection of any flaw indication is very diflicult to remove and cannot be effectively and completely removed by a stream of water alone, as is true of the water-soluble residue left on the surface of the work piece upon evaporation of the water from the present aqueous solution-type developer.

BACKGROUND OF THE INVENTION The field of this invention is the art relating to the nondestructive method of detecting flaws and other surface discontinuities by the liquid penetrant technique. The De Forest et al. Patent No. 2,806,959, owned by the same assignee as the instant application, discloses the use of wet developers comprising suspensions of water-insoluble inorganic particles, such as talc, calcium carbonate, and the like in either an aqueous or an alcohol liquid suspending medium. Since the water-insoluble pigment of the prior art liquid type developers was relied upon to function as the developer by reason of its blotting effect upon the liquid penetrant entrapped in any flaws in the test piece surface, the total omission of any such pigments from the aqueous solution developer of the present invention is clearly an unobvious departure from what was heretofore known by workers in this art.

SUMMARY OF THE INVENTION In the liquid penetrant technique, to which this invention relates, the penetrant can be any of those described in the prior art, including the De Forest et al. Patent No. 2,806,959, but our invention is particularly applicable to the penetrant method in which the liquid penetrant is a water immiscible oil. such as a petroleum hydrocarbon, and contains either a visible or a fluorescent dye dissolved therein.

In accordance with the prent invention, an aqueous solution is prepared for use as a developer by dissolving in water a water-soluble crystalline substance and dispersing therein a surfactant that is compatible with the crystalline substance upon crystallization thereof by the evaporation of water from the solution to deposit upon the surface of the test piece a water-soluble film permeable by the penetrant residue to give it a flaw indication of enhanced visibility in the inspection thereof.

Since the term water-soluble" is a relative term, the use of the term herein will be understood to represent a degree of solubility far in excess of that of the pigments that have heretofore been used in wet developers. In contrast to such pigments as calcium carbonate, talc, and silica, having a water-solubility in general less than about 0.001 gram in 100 cc. of water, the crystalline substances used in the present aqueous solution type developer have a solubility of at least 1 gram in 100 cc. of water at 20 C., and are used in our aqueous solution type developer in a concentration of at least one-half percent by weight up to saturation and even super-saturation concentrations.

The surfactant used with the crystalline substance need not be completely in solution in the developer in the state in which it is used, since some surfactants useful for our purpose give slightly cloudy or even turbid properties to the resulting aqueous solution type developer, but in all cases the surfactant used is one that is compatible with the crystalline substance employed to give, upon evaporation of the water content, a dry deposit that is completely water-soluble. Accordingly, the residue of the dry-deposit formed on the surface of the test piece can be completely removed by washing with water alone, after the inspection step has been completed, so as to leave a clean surface.

In the broadest embodiment of our invention, the aqueous solution developer consists essentially of a watersoluble crystalline substance, which may be either inorganic, organic or metallo-organic, provided it is soluble at least to the extent of one percent by weight; a water dispersible surfactant within the range of from 0.1 to 5% by weight of the solution, which is compatible with the crystalline substance within the definition above given; and optionally a water-soluble film-forming substance within the range of from 0l0%, a water-soluble sequestering agent between the range of from 0 to 5%, a water-soluble corrosion inhibitor within the range of 0 to 5%, and the balance, water.

The following are some of the water-soluble crystalline substances that can be used in our aqueous solution type developer:

Inorganic solubles Sodium nitrate Sodium bicarbonate Sodium carbonate Potassium nitrate Ammonium chloride Potassium iodide Sodium nitrite Inorganic solubles Aluminum chloride Potassium chloride Sodium chloride Organic compounds Urea Sucrose Resorcinol Ethylene diamine tetramine acetic acid, sodium salt Metallo-organic salts Sodium citrate Potassium citrate Ammonium acetate Sodium gluconate Sodium benzoate Sodium salicylate The following are compositions expressed in percentages by weight, of our aqueous solution type developers:

(I) Based upon the use of inorganic crystalline substances:

EXAMPLE 1 Percent Ammonium chloride 10 Triton X114 I L-77 silicone fluid 0.1 Water 88.9

EXAMPLE 2 Percent Potassium nitrate 10 Triton X114 1 L-77 silicone fluid 0.1 Water 88.9

EXAMPLE 3 Percent Sodium bicarbonate 3 Triton X114 1 L-77 silicone fluid 0.1 Water 95.9

EXAMPLE 4 Percent Sodium carbonate 3 Triton X-l14 1 L-77 silicone fluid 0.1 Water 95.9

EXAMPLE 5 Percent Potassium iodide 10 Triton X114 1 L-77 silicone fluid 0.1 Water 88.9

EXAMPLE 6 Percent Sodium nitrite 10 Triton X114 1 L-77 silicone fluid 0.1 Water 88.9

EXAMPLE 7 Percent Aluminum chloride I0 Triton X114 I L-77 silicone fluid 0.1 Water 88.9

EXAMPLE 8 Percent Sodium chloride 10 Triton X114 1 L-77 silicone fluid 0.1 Water 88.9

4 EXAMPLE 9 Percent Potassium chloride 10 Triton X114 l L-77 silicone fluid 0.1 Water 88.9

Trito Xl 14 is just one example of the many surfactants which could be used. Any Water-soluble surfactant stable in the electrolyte medium employed is satisfactory for use. Where sulfur and chlorine content are of concern (because of presenting embrittlement problems) it is desirable to employ surfactants which are free of sulfur and chlorine.

L-77 silicone fluid is a super wetter," and can be used alone, as the surfactant. It is a proprietary product of Union Carbide Corporation, along with other organo silicone surfactants, and is believed to be the reaction product of an organic silicone (siloxane) and a nonionic wetting agent. It is only very slightly soluble in water.

Any of the water soluble crystalline inorganic substances previously listed can be used within the ranges of percentages and in the percentages by weight shown for those in the following:

EXAMPLE 10 Percent Water soluble inorganic substance (to saturation) 1 Surfactant 0.1 to 5 Water Balance EXAMPLE ll, WITH CORROSION INHIBITOR Percent Potassium nitrite l0 Triton X114 l L-77 silicone fluid 0.1 Sodium nitrite 5 Sodium dichromate 0.4 Water 88.5

EXAMPLE 12, WITH SEQUESTERING AGENT Percent Potassium nitrite 10 Triton X114 1 L-77 silicone fluid 0.1 Sodium gluconate 1 Water 87.9

Sodium dichromate protects aluminum from corroding, but does alter to a degree the fluorescense of the indications. In formulations where this is a problem, tetra sodium pyrophosphate can be used and in the same amount.

Other sequestering agents than sodium gluconate can be used.

Examples:

(1) EDTA (2) Versene series (3) Questol series EXAMPLE 13, WITH MIXED WATER SOLUBLE CRYSTALLINE INORGANIC SUBSTANCES Percent Potassium nitrite 10 Sodium bicarbonate 3 Triton X114 1 L-77 silicone fluid 0.1 Water 85.9 EXAMPLE 14, WITH CARBOWAX AS THE FILM FORMER Percent Ammonium chloride 10 Triton X114 l L-77 silicone fluid 0.1 Carbowax 4000 5 Water 83.9

EXAMPLE 15 Percent Sodium bicarbonate 3 Triton X-114 1 L77 silicone fluid 0.1 Carbowax 4000 5 Water 90.9

EXAMPLE 16 Percent Sodium borate 1 Triton X-1l4 1 L77 silicone fluid 0.1 Water 97.9

(II) Based upon the use of water soluble metal or ammonium salts of organic acids:

EXAMPLE 17 Percent Sodium benzoate Triton X-114 1 L77 silicone fluid 0.1 Water 88.9

In place of sodium benzoate in Example 17, sodium salicylate, sodium citrate, potassium citrate, ammonium acetate, sodium gluconate and other water soluble metal or ammonium salts of organic acids can be satisfactorily used in various proportions depending upon their solubilities within the broad limits given herein.

EXAMPLE 18 Percent 2,5 dimethylbenzenesulfonic acid sodium salt 2 Triton X-114 l L77 silicone fluid 0.1 Water 96.9

EXAMPLE 19 Percent 4-amino naphthalenesulfonic acid sodium salt 2 Triton X114 1 L77 silicone fluid 0.1 Water 96.9

Any of the water soluble metal or ammonium salts of organic acids previously listed can be used within the ranges of and in the percentages by weight given in the following:

EXAMPLE 20 Percent Water soluble metal or NH salt of an organic acid (to saturation) 0.5 Surfactant 0.1 to 5 Film former 0 to 10 Water Balance EXAMPLE 21, SPECIFIC MIXTURE Percent Sodium benzoate 10 Sodium gluconate 1 Triton X1l4 1 L77 silicone fluid 0.1 Water 87.9

EXAMPLE 22, SPECIFIC Percent Sodium benzoate 10 Carbowax 4000 2 Triton X-l14 1 L77 silicone fluid 0.1 Water 86.9

EXAMPLE 23 Percent 2,5 dimethylbenzenesulfonic acid sodium salt 2 CarboWax 4000 2 Triton X-1l4 1 L77 silicone fluid 0.1 Water 94.9

(III) Based upon the use of water soluble organic compounds:

EXAMPLE 24 Percent Urea 10 L77 silicone fluid (l.l

Water 89.l

EXAMPLE 25 Percent Sucrose 10 L77 silicone fluid 0.1

Water 89.l

EXAMPLE 26 Percent Resorcinol 5 L77 silicone fluid 0.1

Water 94.9

EXAMPLE 27 Percent 2 butyne 1,4 diol 5 L77 silicone fluid 0.1

Water 94.9

EXAMPLE 28 Percent Acetamide 5 L77 silicone fluid 0.1

Water 94.9

EXAMPLE 29 Hydrazine sulfate l L77 silicone fluid 0.1

Water 98.9

(IV) Based upon the use of a blend of water soluble organic compounds:

EXAMPLE 30 Percent Urea 5 Sucrose 5 L77 silicone fluid 0.l Water 89.9

EXAMPLE 31 Percent Urea 6 Resorcinol 4 L77 silicone fluid 0.1 Water 89.9

(V) Based upon the use of a blend of water soluble organic compounds and inorganic salts:

EXAMPLE 32 Percent Urea 8 Sodium bicarbonate 2 L77 silicone fluid 0.1 Water 89.9

EXAMPLE 33 Percent Urea 8 Sodium nitrite 2 L77 silicone fluid 0.1 Water 89.9

EXAMPLE 34 Percent Urea 5 Potassium nitrate S L77 silicone fluid 0.1 Water 89.9

Surfactants that have been found satisfactory for use in our aqueous solution type developer composition are the following, but in general any surfactant, whether nonionic, cationic or anionic, that is water dispersible, has good wetting properties and is compatible with the other ingredients of the composition to form a completely Water soluble film or lattice deposit, when dried, can be used alone or in combination:

(I) Non-ionic:

(A) Ethoxy fatty alcohols:

(1) Neodol 25-9-Shell Refining Company (2) Neodol 23-6 /zShel] Refining Company (3) Biosoft EA Series-Stepan Chemical Company (B) Alkylphenol polyglycol ethers:

(1) Triton X Seriesisooctyl phenyl polyethoxyethanolsX-l00, Xl02, X1l4Rohm 8L Haas (2) Triton N Seriesnonyl phenyl polyoxyethanols NllRohm & Haas (3) Surfonic N Seriesalkylaryl polyethylene glycol ethersN-60, N-95, N-200, N300Jefferson Chemical Company (4) lgepal CO Seriesnonylphenoxy poly (ethyleneoxy) ethanolGeneral Aniline & Film Company (5) Stepanol B-l29sodium salt of an alkylphenoxy poly oxyethyleneStepan Chemical Comp y (C) Fatty acid esters of polyglycol ethers:

(l) Stepanol TBI(an alkoxypolyoxyethylene ethanolStepan Chemical Company (D) Alkanolamides:

(1) Sole Terge 325-lauric alkanolaminesHod-ag Chemical (2) Sole Terge 59K--mixed fatty alkanolamines Hodag Chemical Company (3) Ninol l281mixed fatty alkanolamines-Stepan Chemical Company (4) Ninol l285fatty acid alkanolamines--Stepan Chemical Company (E) Acetylenic glycols and their ethoxylated derivatives:

(1) Surfynol l04acetylenic glycol 2, 4, 7, 9 tetramethylAirco Chemical (2) Surfynol T.G.a mixture of 5-decyne-4.7 diol. 100% concentration of 104, and an alkylphenyl ether of polyethylene glycol in ethylene glycol surfynol, 83% concentration (F) Ethoxylated fatty acid esters of sorbitan (G) L-77 silicone fluid non-ionic wetting agent-Union Carbide (II) Cationic:

(A) Alkyl aryl quatenary ammonium salts:

(l) Katapone VV328an alkyl polyethoxyethanol benzylammonium chloride, 85% concentration General Aniline & Film Corporation (2) Hyamine 3500N-alkyl (C C C dimethylbenzyl ammonium chlorideRohm & Haas (3) Hyamine 2389-methyl dodecylbenzyl trimethyl dodecyl xylene bis (trimethyl ammonium chloride) 50% concentrationRohm & Haas (4) Ethoquad 0/25polyoxyethylene oleylmethyl ammonium chloride, 95% concentrationArmour Industrial Chemical Company (B) Pyridinium salts:

(l) Emcol E607N lauroyl colamino formyl methyl (pyridium chloride), 90% concentration- Witco Chemical Company, Inc.

([Il) Anionic:

(A) Alkyl aryl sulfonates:

(l) Suframin 85linear alkyl aryl sodium sulfatc Ultra Division of Watco Chemical Company (2) Stepan DS60desalted sodium dodecyl benzene sulfonateStepan Chemical (3) Stepan AAASammonium salt of dodecyl benzene sulfonateStepan Chemical (B) Alkyl sulfonates:

(1) Petroleum sulfonates (C) Alkyl sulfates:

(l) Stepan0lsodium lauryl sulfate series WA-C,

WA, WAQ

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT The preferred water soluble developer composition of our invention, in its dry form, has the following formula, expressed in percentages by weight:

EXAMPLE Percent Sodium benzoate 55.80 Urea 27.90 EDTA 1.12 Carbowax 4000 13.95 L-77 silicone fluid 0.28 Surfonic LF-l7 0.95

Total 100.00

Carbowax 4000 is a proprietary synthetic, Water-soluble wax having a water solubility of 100 grams per 100 cc.

at 20 C. Other members of the Carbowax series of waxes can be used so long as they are water-soluble, non-volatile and preferably solid at room temperature.

In place of Carbowax 4000 as the film-former, other water-soluble film-formers can be used in the same percentage as that given above and within the ranges given in the broader range formulations, such as: hydroxymethyl cellulose (Methocel H6); sodium earboxymethyl-cellulose (CMC); acacia, or gum arabic; bassorin or tragacanthin (the soluble portion of gum tragacanth); Jagar, a product of Stein-Hall & Co., lnc., said to be a natural vegetable colloid from guar seed; and the like. These film-formers act to produce more uniform small size crystals of the crystalline substance used in the resulting film and to cause such film to adhere well to the test piece surface.

EDTA is the abbreviation for ethylene diamine tetraacetic acid. Other sequestering agents, such as those previously named herein can be employed, especially sodium D-gluconate.

L77 silicone fluid has outstanding wetting and spreading characteristics and can be used by itself at extremely low concentrations (0.05 to 0.10%) by weight of the aqueous solution of the selected crystalline substance or mixture of crystalline substances. Other surfactants, such as those already listed herein, can be used in the same percentage as given in Example 35 or Within the broad range of percentages herein given. Where required in order to prevent embrittlement of the metal of the test piece, the surfactant, as well as the other components of our developer composition, should be substantially or wholly free of sulfur and chlorine.

Algaecides and biocides can be added in low concentrations where desirable or required, for example Hyamin 2389, which is water soluble, non-toxic and functions as a cationic wetting agent. It functions particularly well with L77 silicon fluid. Hyamin 2389 is a mixture of methyl-dodecylbenzyl-trimethyl ammonium chloride, 10% methyldodecylxylene bis-trimethyl ammonium chloride as a aqueous solution, and can be used in concentrations of from 10 to 400 ppm.

The dry composition, e.g. that of Example 35, can be diluted with or dissolved in water to any extent within the broad ranges of percent by weight given in the following example:

The higher the bath concentration, especially of the soluble crystalline substance, the brighter are the fluorescent penetrant indications. A workable concentration of the crystalline substance is obtained by using from A lb. of the dry composition per gallon up to as high as saturation, 3 lbs/gal. of water or even higher. An average solution concentration is 1 lb. of the dry composition per gal. of water.

The water soluble developer of our invention has the following advantages over previously known pigmented developers:

1) It is completely removable by the use of water alone, since the residual developer layer or film after drying is completely soluble in water.

(2) Since there are no particles to keep in suspension, there is no need to agitate the developer bath or container.

(3) There is no problem of geilling or thickening of the developer solution in whatever tank or container it is used in.

(4) Since there are no pigment particles, particle size is not a factor with respect to the sensitivity of the color indication and no masking of indications due to agglomeration of particles.

(5) There are no settling or sludging problems.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

We claim:

1. In a method of detecting surface discontinuities in which a liquid penetrant is applied to the surface of a test piece to become entrapped in any discontinuities therein, the excess of penetrant is removed without removal of penetrant residue entrapped in discontinuities and a developer is thereafter applied to said surface to enhance the visibility of flaw indications including said entrapped penetrant residue, the improvement which comprises:

applying as said developer an aqueous solution consisting essentially of a water-soluble crystalline substance present in an amount of at least 0.5% by weight up to saturation, and

a water dispersible surfactant compatible with said water-soluble crystalline substance and present in an amount from 0.1% to 10% by weight of said solution; said water dispersible surfactant being compatible with said water-soluble crystalline substance upon crystallization of the latter by evaporation of Water from said solution to deposit on said test piece surface a water soluble crystalline film permeable by said penetrant residue to give a flaw indication of enhanced visibility upon inspection thereof.

2. The method as defined by claim 1, in which,

said liquid penetrant is an oil, and

said surfactant is miscible with said oil to effect migration of said penetrant residue into said water soluble film.

3. A method as defined by claim 1, in which said water soluble crystalline substance is an organic compound soluble in water to the extent of 10% by weight of the resulting solution.

4. A method as defined by claim 1, in which said water soluble crystalline substance is an inorganic salt.

5. A method as defined by claim 1, in which said water soluble crystalline substance is a metal salt of an organic acid.

6. A method as defined by claim 1, in which after inspection of said flaw indication said film is removed by water washing to leave a clean surface.

7. A method as defined by claim 1, in which said water soluble crystalline substance is present in an amount of at least 1% by weight, and said surfactant is present in the range of from about 0.1% to 10% by weight of said aqueous solution.

8. A method as defined by claim 1, in which said aqueous solution has a composition within the following proportions by weight of the solution:

water-soluble crystalline substance from 0.5% to saturation.

water-soluble surfactant from 0.1% to 5%, water-soluble film-forming substance from to 10%,

water-soluble sequestering agent from 0 to water-soluble corrosion inhibitor from 0 to 5 and the balance water, said solution upon evaporation leaving a penetrant permeable crystalline film removable by water washing alone.

9. A method as defined by claim 8 wherein,

said water-soluble crystalline substance is sodium benzoate, and

said water-soluble film-forming substance is a normally solid, non-volatile water-soluble wax having a water solubility of 100 grams per 100 cc. at 20 C.

10. An aqueous solution for use as a water-soluble developer in the liquid penetrant method of detecting surface discontinuities in a test piece, consisting essentially of the following:

at least 1% of a mixture of sodium benzoate and urea,

from 0.1% to 5% of a surfactant,

from 0 to 10% of a water-soluble film-former that is non-volatile and solid at room temperature, and the balance water, said solution upon evaporation of the water leaving a water-soluble crystalline film permeable by the liquid penetrant to form a flaw indication of enhanced visibility upon inspection thereof.

11. A water-soluble developer for use in the liquid penetrant method of detecting surface discontinuities in a test piece, comprising an aqueous solution consisting essentially of the following:

from 0.5% to saturation and above of sodium benzoate,

from 0.1% to 10% of a water dispersible surfactant,

a water-soluble film-forming, normally water-soluble wax in an amount up to 10% and sufficient to produce uniformly sized small crystals of said sodium benzoate, from 0 to 5% of a corrosion inhibitor, and the balance being largely water, said solution upon evaporation of the water leaving a water-soluble crystalline film permeable by the liquid penetrant to form a fiaw indication of enhanced visibility upon inspection.

12. An aqueous solution for use as a water-soluble developer in the liquid penetrant method of detecting surface discontinuities in the test piece, consisting essentially 0 of the following:

from 0.5% to saturation of a crystalline water-soluble metal or NH, salt of an organic acid, from 0.1% to 5% of a surfactant, and up to 10% of a water-soluble film-forming, normally solid, non-volatile wax having a water solubility of 100 grams per 100 cc. of water at 20 C. in an amount sufficient to produce uniform small sized crystals of said crystalline salt, the balance being largely water and said solution upon 7 evaporation of said water leaving a water-soluble crystalline film permeable by said liquid penetrant to form a flaw indication of enhanced visibility upon inspection thereof.

(References on following page) References Cited UNITED STATES PATENTS Lemmerman et a1. 252-351 Winning et a1. 252-351 Vitalis 252-3635 Vitalis 252-152 Soule et a1. 252-152 Stephan 252-152 Mains et a1. 252-152 Compton 252-152 Lamberti 252-35] Alburger 250-71 Hirota et a1 73-40 Kakegawa et a1. 252-89 12 FOREIGN PATENTS 7/1949 Canada 254-71 OTHER REFERENCES TOBIAS E. LEVOW, Primary Examiner A. P. DEMERS, Assistant Examiner US. Cl. X.R.

UNI'IEI) S'IA'II'IS PA'IEN'I ()FFNIE CER'IIFICA'IE ()F (IORREC'PION Patent No. 3, 561, 262 Dated February 9 1971 Inventor(s) James S. Borucki 81 Bruce C. Graham It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 14, cancel "prent" and substitute --present--.

Col. 4, lines 28 81 29, cancel "(to saturation)", and in the column headed by "Percent", after "1" insert --to saturation-.

Col. 4, in Examples 11, 12 and 13, first line under each example, cancel "nitrite" and substitute -nitrate--.

C01. 5, under Example 20, line 49, cancel "(to saturation)" and, same line, after "0.5" add --to saturation--.

C01. 8, line 71, cancel "silicon", and substitute --silicone--.

Col. 9, line 31, correct the spelling of -gel1ing--.

Signed and sealed this 12th day of October 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pate 

